The present invention relates to metal cutting inserts having a round cutting edge.
Cutting inserts are conventional which possess a top (chipbreaking) surface and a frusto-conical edge (clearance) surface which intersects the top surface to form therewith a round cutting edge. Such inserts, usually formed of a cemented carbide, are used in copy turning operations and making rounded fillets. A central through-hole in the insert receives a fixing screw which is connectible to a threaded hole in a holder to anchor the insert in place. The holder defines a tip seat or pocket in which the insert is received. The pocket includes an upstanding locating wall which is generally V-shaped when viewed in plan, whereby the frusto-conical edge surface makes contact with that locating wall at two locations. During a cutting operation, only a portion of the round cutting edge actually cuts the workpiece. When that portion is worn, the insert is indexed to present a fresh portion of the cutting edge for cutting. It is important that, during the cutting operation, the insert remain fixed against rotation (slippage) about its center axis relative to the holder. However, due to the curvature of the edge surface of the insert, such slippage may occur, despite being pressed tightly against the locating wall by the fixing screw. It is a goal of the present invention to prevent such slippage without weakening the cutting edge.
In Raupp, Jr. et al U.S. Pat. No. 4,273,479, an indexable broaching insert is described which includes a cylindrical edge surface that intersects a top (clearance) surface to form a round cutting edge. The cylindrical surface includes four equi-spaced flats which make engagement with a locating wall for resisting slippage of the broaching insert during cutting. The flats are oriented parallel to the center axis of the insert and intersect the cutting edge to convert what would otherwise be a round cutting edge into a polygonal cutting edge. Such a polygonal cutting edge, however, would not be suitable for copy turning and fillet making.